Purge cycles for precipitator



May 20, 1958 P. HoDsoN PURGE CYCLES FOR PRECIPITATOR Filed Aug. 3, 1955 United States Patent() PURGE CYCLES FOR PRECIPITATOR Peter Hodson, Weilsville, N. Y., assignor to Apra Precipitator Corporation, New York, N. Y., a corporation of Delaware Application August 3, 1955, Serial No. 526,260

9 Claims. (Cl. 183-7) The present invention relates generally to a gas cleaning system and especially it relates to iiow cycles eiective in removing deposits of dust from collecting surfaces within an electrostatic precipitator.

In a gas cleaning system of the type herein defined, a mechanical pre-collector receives the full iiow of a contaminated gas stream being directed into an electrostatic precipitator. The mechanical pre-collector is of a type removing only relatively large easily removed particles from the gas stream at little loss of pressure thereto.

The contaminated gas stream containing only the relatively small particles or fines leaves the pre-collector and is passed on to the precipitator where the fines are removed from the gas stream by a process of electrostatic precipitation.

As the fine dust particles are deposited upon the dust collecting surfaces within the precipitator, a coating of deposits builds up toimpair thecollecting eiiiciency of the `surface thereby necessitating frequent removal of the dust deposits to maintain a high collecting eiiiciency. Various cleaning arrangements for the removal of deposited dust particles have been devised including mechanical scraping and rapping means together with forcing a cleaning fluid over the surfaces on which the dust i particels have collected, and this invention is directed to a complete purge cycle for the removal of collected dust particles 'from a collectingr `surface by a process involving drawing a stream of purge gas over the surfaces to be v cleaned together with subsequent cleaning of the purge gas.

For a better understanding of the invention, reference to the accompanying drawings may be had in which:

Figure l is a diagrammatic illustration of a purging system for an electrostatic precipitator wherein the purge gas is circulated independent of the main gas tlow.

Figures 2, 3, and 4 diagrammatically illustrate various moditications of a purging system for an electrostatic precipitator Where the purging fluid is obtained from the main gas iiow in advance of the precipitator.

Figures 5 and 6 diagrammatically illustrate several modifications of purging system for an electrostatic precipitator where the purging iiuid is obtained from the main gas iiow subsequent to the precipitator.

In the drawings numeral 10 indicates an electrostatic precipitator comprising a mass of collecting elements having an inlet duct 12 in which a mechanical pre-collector 14 is positioned to remove large readily removable particles from the liuid stream owing into the precipitator. A second inlet duct 16 leading to precipitator 10 directs a purging fluid to and through a group of collecting elements isolated from the main stream of gas, various groups of elements being successively purged so that the collector is continuously cleaned of collected particles. The purging fluid is drawn from outlet duct 18 through an after-collector 20 by a fan 24, the after-collector being effective to remove the great bulk of the particles which are relatively large due to agglomeration in the precipi- ICC tator, from the purge fluid so that it may be returned to the precipitator without extreme contamination.

Figure l illustrates a purge cycle where the purge gas is maintained entirelypseparate from the main gas flow since the outlet from after-collector 20 leads through fan 24 directly to purge gas inlet duct 16. Auxiliary lines 26 and 28 maybe installed in the system to provide make-up uid from the main fluid supply duct to replace iuid lost from the purge system, especially that lost in the precipitator or to bleed ot excess iluid. Any dust not deposited in the after-collector is recirculated so it cannot reenter the main gas stream and reach the outlet stack.

In Figures 2, 3 and 4 iiuid for purging is drawn from the main fluid flow line and after traversing the precipitator and the after-collector 20, it is returned to the inlet duct 12 of the main flow line. Figurel 2 represents a purge cycle wherein the purging iiuid is drawn from the main duct at a point between the precipitator and the precollector 14 and is returned to an adjacent point. Here any dust not collected by the after-collector 20 is treated again in the precipitator so that little dust is lost to the atmosphere.

lf the gas cleaning system operates at a comparably low level of dust loading, the mechanical pre-collector may be entirely omitted from the cycle of operation without any adverse effects.

Figure 3 illustrates a purging cycle similar to that of Figure 2 except that the relatively clean purge gas from after-collector 20 is still further treated by a pre-collector 14 before it is returned to the precipitator'. This form has the added advantage in effect, of increasing the eiiiciency of the pre-collector 14 and thereby increasing the eiiiciency of the purging fluid within the precipitator 10; lf purging iluid is taken from a point in advance of the precollector 14, and after traversing the purging cycle, is returned to a similar point as illustrated in Figure 4, the size of pre-collector 14 utilized in the cycle may be reduced because of reduced iiuid flow, however, the quality of cleaning operation within the precipitator will be somewhat reduced because the purging fluid is initially laden with dust particles from the main fluid stream.

lf the purge gas is drawn from the clean gas stream emerging from the precipator and is returned to a point in inlet duct 12 between the precipitator 10 and precollectorlt in the manner illustrated in Figure 5, a portion of the dust escaping the precipitator is treated again in the after-collector 20 and the precipitator 10 to improve the overall cleaning eiciency of the cycle. This cycle may be further modified as shown in Fig. 6 by re-` turning the purge gas from the after-collector 20 to a point in advance of pre-collector 14 so that the dust loading of the gas entering the `precipitator may be further reduced.

Each of the purging cycles above defined oiers particular advantage of design or eiiiciency of operation that are dependent upon speciiic conditions encountered, and it is vevident that the invention is applicable to many different structural arrangements and combinations of apparatus employed for precipitator purging systems. It is therefore understood that this invention embraces all forms and arrangements of operation that `fall within the preview of the appended claims.

What I claim is:

l. A purging system for an electrostatic precipitator having collecting elements between main inlet and outlet ducts comprising; purging gas inlet and outlet ducts connected to said precipitator to direct the iiow of purging gas to and through the collecting elements thereof; a gas cleaning device arranged to receive dust laden purging gas from the purging gas outlet; and means returning relatively dust free gas from the gas cleaning device to the main gas inlet of said precipitator.

2. A purging system for an electrostatic precipitator having a main inlet and outlet including a pre-collector in advance of said main inlet comprising; a purging inlet `'and outlet in said precipitator directing the flow of purging iluid to and through a 'mass of cleaning elements thereof; an after-collector arranged to receive dust laden purging fluid from the purging uid outlet leading from said precipitator; and duct means interconnecting said after collector and the main inlet to the precipitator.

3. A purging system for an electrostatic precipitator containing cleaning elements between a main gas inlet duct and an outlet duct comprising; a purging gas inlet and outlet arranged to direct the ow of purging gas from the main gas inlet duct to and through the cleaning elements of the precipitator; a gas cleaning device arranged to receive dust laden purging gas from said purgingwgas outlet; and duct means returning relatively dust free purging fluid from the gas cleaning device to said main gas inlet duct.

4. A kpurging system for an electrostatic precipitator containing cleaning elements between a main gas inlet and `an outlet therefor including a mechanical pre-collector in advance of said inlet comprising; a purging gas inlet and outlet in the pricipitator to direct the ow of purging gas from a point in advance of said precipitator to and through the cleaning elements thereof; an after-collector arranged to receive dust laden purging fluid from the purging fluid outlet leading from said precipitator; and means directing relatively dust free purging iluid from the aftercollector to the main gas inlet to the precipitator.

5. A purging system for an electrostatic precipitator as defined in claim 4 wherein the purging fluid is withdrawn from and return to said main gas inlet duct intermediate the electrostatic precipitator and mechanical precollector.

6. A purging system for an electrostatic precipitator as defined in claim 4 wherein the purging fluid is with- CII drawn from the main gas inlet duct intermediate the electrostatic precipitator and mechanical pre-collector and is returned to said main gas inlet duct in advance of said mechanical pre-collector.

7. A purging system for an electrostatic precipitator as dened in claim 4 wherein the purging fluid is withdrawn from and returned to said main gas inlet duct in advance of said mechanical pre-collector.

8. A purging system for an electrostatic precipitator having cleaning elements intermediate main gas inlet and outlet ducts comprising purging gas inlet and outlet ducts connected to said precipitator to direct the low of purging gas from a point adjacent the main gas outlet to and through the cleaning elements thereof; a gas cleaning device arranged to receive dust laden purging gas from the purging gas outlet; and duct means directing relatively dust free gas from the gas cleaning device .to the main gas inlet.

9. A purging system for an electrostatic precipitator remaining collecting elements intermediate a main gas inlet and an outlet therefor and havinr a pre-collector in advance of `said inlet comprising; purging gas inlet and outlet ducts connected to said precipitator arranged to direct purging gas from the main gas outlet through the collecting elements of the precipitator in `a parallel opposed relation to the main gas ilow; an after-collector arranged to receive dust laden purging gas from the purging gas outlet; and means directing relatively dust free purging gas from the after-collector to the main gas inlet in advance of said pre-collector.

References Cited in the le of this patent UNITED STATES PATENTS 2,701,622 Hodson' Feb. s, 1955 FOREIGN PATENTS 562,628 Germany oct. 27, 1932 

